This invention relates to a heat and moisture exchanging device for respiration suitable for conducting general anesthesia, artificial respiration, etc. The device according to this invention is capable of adjusting appropriately the physical conditions of the inhaling air and, at the said time, observing the number of breaths per unit time, respired air volume and the volume of tidal air.
Where general anesthesia or artificial respiration is applied to a patient, one end of the tracheal cannula is inserted into the trachea and the other end connected to an anesthetizing device or a respirator. In this case, the mucous membrane of the upper portion of the respiratory tract loses its physiologial air conditioning function which would be performed in normal respirations. Namely, in normal respirations, heat and moisture of the exhaling air are absorbed by the inner walls of nasal cavities, oral cavity and pharynx and a major part of the heat and moisture thus absorbed is imparted to the inhaling air so as to make it suitable for inhalation.
However, where a tracheal cannula is inserted into the trachea for respirations, the exhaling air comes out of the human body hot and humid and the inhaling air is scarcely warmed nor moistened, because the inner wall of the cannula is smooth and, thus, inferior in capabilities of moisture absorption and heat exchange. It follows that the application of an anesthetizing device or a respirator for a long time causes the respiratory tract of the patient to be dried, giving the patient hard pains. In some cases, lung diseases are possibly caused.
To solve the problem, conventional devices for general anesthesia or artificial respiration utilize moistening means such as nebulizer so as to moisten the inhaling air appropriately. But, where, for example, a nebulizer is used in an anesthetizing device of a closed circulation type, it is undesirable to add excessive moisture to the inhaling air because the carbon dioxide absorbing agent used in the anesthetizing device is hygroscopic in nature. When used in a respirator, it is difficult for the nebulizer always to impart appropriate moisture to the inhaling air.
Also known is a device using aluminum foils for recovering the moisture and heat of the exhaling air (see Acta anaesth, Scandinav. 1960, 4, pages 105-124, "POSTOPERATIVE CARE AND COMPLICATIONS AFTER TRACHEOTOMY IN INFANTS AND CHILDREN"). This device, however, fails to give a satisfactorily sharp temperature gradient across the heat exchange body. Thus, a large dead space is required for sufficiently recovering moisture and heat from the exhaling air.
It should also be noted that, where a tracheal cannula is used for conducting a medical operation or applied to a patient with an advanced disease, it is necessary to check the number of breaths per unit time, respired air volume and the volume of tidal air besides the warming and moistening problems described. For observation of the number of breaths per unit time, known is a method in which is used a thermistor placed inside the nasal cavities or mounted at the outer end of a tracheal cannula. In this case, the number of breaths is measured from the temperature changes of the respiratory air detected by the thermistor. This method, however, fails to measure the volume of tidal air. Hot wire anemometers or the like are available for the measurement of the volume of tidal air. But, any of conventional devices is unsuitable for services for a long time. Particularly, inconveniences in sterilization are a nuisance.